In the failure analysis of electronic structures, a specimen that contains a defect is frequently prepared for microscopic examination. For instance, a specimen of an electronic structure such as a semiconductor wafer may be analyzed in a scanning electron microscope (SEM) or a transmission electron microscope (TEM) to study a characteristic feature in the semiconductor device. The characteristic feature may be a circuit fabricated or a defect formed during the fabrication process. SEM is one of the most useful equipment for analyzing the microscopic structure of semiconductor devices since it is capable of providing a three-dimensional image on a specimen that can be simply prepared.
In preparing a specimen of a semiconductor wafer for electron microscopic examination, various polishing and milling processes are used for sectioning a structure until a specific characteristic feature is exposed. As device dimensions are continuously reduced to the sub-half-micron level, the techniques used for preparing specimens for study in an electron microscope have become more important. The conventional method of studying structures in an optical microscope cannot be used to study features in a modem electronic structure due to its low resolution.
Generally, when a specimen is prepared for an electronic microscopic observation of a characteristic feature, various polishing and grinding techniques are used to first bring the dimensions of a specimen down to a size just before the characteristic feature is revealed. A final sample preparation step is then carried out in a method such as ion milling by a focused ion beam (FIB) technique.
In a FIB technique, focused ion beams are used to locally remove materials. A cluster of an ionized beam consists of an aggregate of from 100 to 2,000 atoms is aimed at a sample surface. When the cluster impacts the surface of the electronic structure, the cluster disintegrates into atoms which are them scattered over the surface to remove a surface layer of the material. While the FIB technique is effective in preparing a specimen the microscopic examination of a semiconductor wafer, the cross-section prepared which contains the structural feature, or the defect, is frequently blurred and does not present a sharp contrast. This results in a micrograph of poor resolution. Moreover, the cost of a FIB equipment is high such that it cannot be provided at every fabrication facility. It is therefore desirable to provide a simple method for specimen preparation that can be carried out at a fabrication facility inexpensively.
It is therefore an object of the present invention to provide a method for preparing a semiconductor specimen that does not have the drawbacks or shortcomings of the conventional methods.
It is another object of the present invention to provide a micro-cleavage method for preparing a semiconductor specimen that can be performed manually without using expensive equipment.
It is a further object of the present invention to provide a micro-cleavage method for preparing a semiconductor specimen for optical microscope or electronic microscope observation.
It is another further object of the present invention to provide a micro-cleavage method for preparing a semiconductor specimen that only requires the use of a diamond knife and a laser cutter.
It is still another object of the present invention to provide a micro-cleavage method for preparing a semiconductor specimen wherein bird's beak-shaped marks are first made on a wafer surface.
It is yet another object of the present invention to provide a micro-cleavage method for preparing a semiconductor specimen by making bird's beak-shaped marks on the surface of a wafer such that a large base portion of the mark can be used for visual alignment, while a small tip portion of the mark can be used for initiating a crack.
It is still another further object of the present invention to provide a micro-cleavage method for preparing a semiconductor specimen wherein at least two bird's beak-shaped marks are cut into a surface of a wafer with one mark positioned juxtaposed to a wafer edge and at least one other mark positioned juxtaposed to a target to be observed.
It is yet another further object of the present invention to provide a micro-cleavage method for preparing a semiconductor specimen by first providing at least two bird's beak-shaped marks on a top surface of the wafer, then position the wafer on a straight ruler with the bird's beakshaped marks facing up, and then bending down the wafer surface to initiate a crack through a target to be observed.